The Japanese philosophy on knife making is different from Western mass market knives. They tend to temper their knives so they are harder. This makes them hold an edge longer but also makes them harder to sharpen and a bit more brittle. The harder temper also allows them to sharpen their knives at a more acute angle.They also still make quite a few knives using carbon steel vs stainless steel. Their knives are superior for these reasons, as long as you can deal with the fact that they are harder to sharpen.
I don't own any myself, but my daughter has a Japanese mass market knife I am eager to try out on my next visit. I may have to impose a voluntary ban on getting one similar to Moikel's
EBay ban because most knife connoisseurs consider them to be the best and as you can see from my collection once I start I may be unable to stop.
Re the guy using WWII scrap, the Forgecraft knives I pictured were made out of old Sawmill blades.